linux-kernel - Re: 2.6.32-rc5-mmotm1101 - lockdep whinge during early boot

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Message-ID: <alpine.LFD.2.00.0911051547110.12138@localhost.localdomain>
Date:	Thu, 5 Nov 2009 15:54:48 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Rusty Russell <rusty@...tcorp.com.au>, Valdis.Kletnieks@...edu,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: 2.6.32-rc5-mmotm1101 - lockdep whinge during early boot

On Thu, 5 Nov 2009, Oleg Nesterov wrote:
> > Oleg (CC'd) made workqueues use cpu_maps_update_begin() instead of the
> > more obvious get_online_cpus() in 3da1c84c00c7e5f.  Reverting that seems like
> > a bad idea.
> 
> Even if create_workueue() used get_online_cpus() instead of cpu_add_remove_lock,
> we have the same problem: _cpu_up() takes cpu_hotplug.lock which is needed for
> get_online_cpus(). The dependency above becomes:
> 
> 	cpu_up()->clocksource_change_rating() takes clocksource_mutex under
> 	cpu_hotplug.lock (cpu_hotplug_begin)
> 
> 	clocksource_done_booting()->create_workueue() takes cpu_hotplug.lock
> 	(get_online_cpus) under clocksource_mutex

Hmm, we fixed all this lock madness in mainline already.
clocksource_done_booting() does not longer call
create_workqueue(). How got this code reverted in motm ?

Thanks,

	tglx
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